U.S. patent number 7,179,541 [Application Number 10/481,289] was granted by the patent office on 2007-02-20 for heat treatment method for a cold-rolled strip with an ni and/or co surface coating, sheet metal producible by said method and battery can producible by said method.
This patent grant is currently assigned to Hille & Muller GmbH. Invention is credited to Claudia Dahmen, Beate Monscheuer, Werner Olberding, Karlfried Pfeifenbring.
United States Patent |
7,179,541 |
Olberding , et al. |
February 20, 2007 |
Heat treatment method for a cold-rolled strip with an Ni and/or Co
surface coating, sheet metal producible by said method and battery
can producible by said method
Abstract
A method for heat treatment of a cold rolled strip with a
surface coating of Ni and/or Co and incorporated non-metallic
elements C and/or S, if need be with the addition of Fe, In, Pd, Au
and/or Bi, whereby the cold rolled strip has a low carbon content.
Since the compounds of C, S, N and P deposited on the grain
boundaries bring about the most micro-cracks with the surface
coating metal if no recrystallization takes place, the temperature
of the heat treatment should be selected lower than the
recrystallization temperature and higher than the precipitation
temperature. With a recrystallization, the grain sizes would easily
attain the thickness of the coating so that the embrittled
compounds would migrate with the grain boundaries out of the
coating. Due to the choice of temperature of the heat treatment of
the surface coating of the invention, in contrast, an optimal
embrittlement of the grain boundaries is guaranteed, which is
especially advantageous in the manufacture of battery cans.
Furthermore the sheet metal which can be manufactured in accordance
with the invention and the corresponding battery can are
described.
Inventors: |
Olberding; Werner (Velbert,
DE), Monscheuer; Beate (Monheim, DE),
Dahmen; Claudia (Viersen, DE), Pfeifenbring;
Karlfried (Duisburg, DE) |
Assignee: |
Hille & Muller GmbH
(DE)
|
Family
ID: |
7688928 |
Appl.
No.: |
10/481,289 |
Filed: |
June 12, 2002 |
PCT
Filed: |
June 12, 2002 |
PCT No.: |
PCT/EP02/06431 |
371(c)(1),(2),(4) Date: |
July 02, 2004 |
PCT
Pub. No.: |
WO03/000937 |
PCT
Pub. Date: |
January 03, 2003 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20040238078 A1 |
Dec 2, 2004 |
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Foreign Application Priority Data
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Jun 21, 2001 [DE] |
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101 29 900 |
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Current U.S.
Class: |
428/679; 148/537;
205/228; 428/935; 429/163; 427/383.7; 205/227; 148/518 |
Current CPC
Class: |
C25D
3/14 (20130101); H01M 50/116 (20210101); C25D
5/50 (20130101); C21D 9/48 (20130101); C23C
28/027 (20130101); C25D 7/00 (20130101); C23C
28/028 (20130101); H01M 50/1243 (20210101); C23C
28/021 (20130101); C23C 28/023 (20130101); C21D
8/0478 (20130101); Y02E 60/10 (20130101); Y10T
428/12937 (20150115); Y10S 428/935 (20130101); H01M
50/124 (20210101) |
Current International
Class: |
H01M
2/02 (20060101); B32B 15/01 (20060101); C22F
1/10 (20060101); C25D 5/50 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
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4302256 |
November 1981 |
Kenton |
4908280 |
March 1990 |
Omura et al. |
4910096 |
March 1990 |
Junkers et al. |
5993994 |
November 1999 |
Ohmura et al. |
6126759 |
October 2000 |
Hosoya et al. |
6613163 |
September 2003 |
Pfeifenbring et al. |
6852445 |
February 2005 |
Schmidt et al. |
6982011 |
January 2006 |
Pfeifenbring et al. |
|
Foreign Patent Documents
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1137332 |
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Dec 1996 |
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CN |
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0 725 453 |
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Aug 1996 |
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EP |
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WO 01/11114 |
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Feb 2001 |
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WO |
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Primary Examiner: Zimmerman; John J.
Attorney, Agent or Firm: Cantor Colburn LLP
Claims
The invention claimed is:
1. Method for a heat treatment of a cold rolled strip the method
comprising: selecting a temperature of the heat treatment that is
less than a recrystallization temperature of a surface coating and
above a precipitation temperature for compounds that accumulate on
grain boundaries and include non-metallic elements and surface
coating metal, wherein the surface coating comprises Ni and/or Co
and non-metallic elements C and/or S, and wherein the cold rolled
strip has a carbon content.
2. Method according to claim 1, wherein the carbon content of the
cold rolled strip is less than 0.5%.
3. Method according to claim 1, further comprising applying a
prefinishing layer of Ni and/or Co or of a multilayer system of
these elements to the cold rolled strip before surface coating.
4. Method according to claim 3, wherein the prefinishing layer is
diffusion-annealed.
5. Method according to claim 3, wherein the applying includes
applying the prefinishing layer using diffusion precipitation.
6. Method according to claim 3, wherein the applying includes
applying the prefinishing layer as a C--Ni dispersion layer or a
C--Ni/Co alloy dispersion layer.
7. Method according to claim 4, further comprising applying a
dispersion coating and a surface coating after the
diffusion-annealed prefinishing layer.
8. Method according to claim 7, wherein the dispersion layer is
applied as a C--Ni dispersion layer or as a C--Ni/Co alloy
dispersion layer.
9. Method according to claim 1, wherein instead of C and S, P is
incorporated as a non-metallic element into the surface coating, or
a mixture of P, C and/or S.
10. Method according to claim 1, wherein instead of C and S, N is
incorporated as a non-metallic element into the surface coating, or
a mixture of N, C and/or S and/or P.
11. Method according to claim 1, wherein the surface coating is
selectively embrittled according to the incorporated non-metallic
component through heat treatment.
12. Method of claim 1, wherein the surface coating further
comprises Fe, In, Pd, Au and/or Bi.
13. Sheet metal of low carbon content suitable for a deep drawing
process, the sheet metal comprising: a cold rolled strip coated
with a surface coating of Ni and/or Co embrittled by temperature
treatment and incorporated non-metallic elements C and/or S, the
surface coating has a large number of micro-cracks following a deep
drawing or an iron drawing, wherein the surface coating is not
recrystallized by the heat treatment and compounds of non-metallic
elements are accumulated on grain boundaries with the surface
coating material.
14. Sheet metal according to claim 13, wherein the low carbon
content of the cold rolled strip is less than 0.5%.
15. Sheet metal according to claim 13, further comprising a
prefinishing layer between the cold rolled strip and the embrittled
surface coating that includes Ni and/or Co or of a multilayer
system of these elements.
16. Sheet metal according to claim 15, wherein the prefinishing
layer is diffusion-annealed.
17. Sheet metal according to claim 15, wherein the prefinishing
layer is a dispersion layer.
18. Sheet metal according to claim 15, wherein the prefinishing
layer is a C--Ni dispersion layer or a C--Ni/Co alloy dispersion
layer.
19. Sheet metal according to claim 16, wherein a dispersion layer
is applied between the diffusion-annealed prefinishing layer and
the embrittled surface coating.
20. Sheet metal according to claim 19, wherein the dispersion layer
is a C--Ni dispersion layer or a C--Ni/Co alloy dispersion
layer.
21. Sheet metal according to claim 13, wherein instead of C and S,
P is incorporated as a non-metallic element in the embrittled
surface coating, or a mixture of P, C and/or S.
22. Sheet metal according to claim 13, wherein instead of C and S,
N is incorporated as a non-metallic element in the embrittled
surface coating, or a mixture of N, C and/or S and/or P.
23. Sheet metal according to claim 13, wherein the surface coating
is selectively embrittled by the temperature treatment according to
the included non-metal component.
24. Sheet metal of claim 13, wherein the surface coating further
comprises Fe, In, Pd and/or Bi.
25. Battery can of low carbon content suited for the deep drawing
process, the battery can comprising: a cold rolled strip coated
with a surface coating of Ni and/or Co and incorporated
non-metallic elements C and/or S, located on an inside embrittled
and after a temperature treatment, the surface coating has a large
number of micro-cracks following a deep drawing or stretch deep
drawing, wherein the surface coating is not recrystallized by the
heat treatment and compounds of non-metallic element with the
surface coating material are deposited on the grain boundaries.
26. Batter can according to claim 25 wherein the low carbon content
of the cold rolled strip is less than 0.5%.
27. Battery can according to claim 25, wherein the cold rolled
strip has a prefinishing layer between the cold rolled strip and
the embrittled surface coating which consists of Ni and/or Co or of
a multilayer system of these elements.
28. Battery can according to claim 27, wherein the prefinishing
layer is dispersion-annealed.
29. Battery can according to claim 27, wherein the prefinishing
layer is a dispersion layer.
30. Battery can according to claim 27, wherein the prefinishing
layer is a C--Ni dispersion layer or a C--Ni/Co alloy dispersion
layer.
31. Battery can according to claim 28, wherein a dispersion layer
is applied between the diffusion-annealed prefinishing layer and
the embrittled surface coating.
32. Battery can according to claim 31, wherein the dispersion layer
is a C--Ni dispersion layer or a C--Ni/Co alloy dispersion
layer.
33. Battery can according to claim 25, wherein instead of C and S,
P is incorporated as a non-metallic element in the embrittled
surface coating, or a mixture of P, C and/or S.
34. Battery can according to claim 25, wherein instead of C and S,
N is incorporated as a non-metallic element in the embrittled
surface coating, or a mixture of N, C and/or S and/or P.
35. Battery can of claim 25, the surface coating further comprises
Fe, In, Pd, Au and/or Bi.
Description
FIELD OF THE INVENTION
The invention concerns a method for heat-treating a cold rolled
strip with a surface coating of Ni and/or Co and integrated
non-metallic elements C and/or S, if need be with the addition of
Fe, In, Pd, Au and/or Bi, whereby the cold rolled strip has a low
carbon content.
DESCRIPTION OF THE RELATED ART
It is known from the literature that the hardness of coatings can
be increased by selective temperature treatment. This leads to an
increase in hardness and brittleness and to a generally undesirable
tearing of coatings during forming. In contrast, this effect is
desirable in manufacturing battery cans.
Galvanic (electrolytic) and autocatalytic coatings are known
coating methods whereby the most frequent coatings are Ni or Co
coatings, or coatings of other alloys. Most frequent are Ni
coatings, on the basis of which the following explanations are
being made, which, however, also apply for other similar
coatings.
In electrolytic coating, a current is applied to the material to be
coated which dips into a solution containing Ni ions. The nickel is
converted into metallic nickel and forms a coating on the material.
If organic substances are admixed to the treatment bath then the
coating is precipitated with another morphology, which leads to a
harder layer and to a glossy appearance of the layer. Degradation
products of organic substances are incorporated into the layer. In
general, it is C or S, but N and P are also possible.
The type of autocatalytic Ni coating has several names which all
describe the same process: "Autocatalytic," "external currentless"
or "chemical nickel-plating." In this method, the nickel is not
converted into metallic nickel by "current," but a substance is
added to the treatment bath, which supplies the electrons necessary
for the conversion. Generally a phosphorus-containing substance is
used for this reaction. Degradation products of this
phosphorus-containing substance are incorporated into the layer,
and indeed in a basically higher concentration than C and S in the
electrolytic bright nickel bath (6 to 12% in comparison to 0.001 to
0.1%). It is known that these phosphorus-containing layers are very
hard and that their hardness can be increased by temperature
treatment. However the precipitation rate of this method is
considerably slower than that of galvanic nickel plating, and for
this reason, the autocatalytic coating is in many cases
disadvantageous from a commercial perspective.
Basically all known bath types can be selected for applying the
layer for galvanic coating. Let merely the so-called Watts bath and
the sulfamate bath be mentioned here as examples for
nickel-plating. These baths are also suitable for applying Co or
Co/Ni alloy coatings in modified form.
The publication "Electrolytically Separated Nickel Layers-Influence
of the Sulfur Content of Hardness and Ductility" (Kreya et al., p.
584 587, 1995) appeared in the trade journal Metal Surface 49. It
is oriented around the precipitation of nickel for the manufacture
of stamping foils. The content of the publication is the
embrittlement by temperature treatment of Ni layers, which were
precipitated out of sulfamate baths. It was established that
sulfur-containing layers become embrittled following temperature
treatment above the recrystallization temperature in that the
sulfur accumulates on the grain boundaries. It is suspected that
the accumulated sulfur is carried along with the migration of the
grain boundaries. The annealing temperature above which an
embrittlement takes place in the layers separated from saccharin
(sulfur-containing compound in the electrolyte) depends upon the
sulfur content in the layer and begins at about 250.degree. C. to
350.degree. C. It has furthermore been established that
additionally incorporated manganese avoids an embrittlement of the
layer.
The publication "Chemical Nickel Layers-Properties and Layer
Combinations" (Electroplating 53, page 34 36, 1999) describes how
the formation of Ni.sub.3P crystals occurs due to a heat treatment
of external currentless, precipitated Ni layers, wherein said
crystals bring about a mixed crystal hardening. In contrast to
this, galvanically separated Ni layers behave otherwise. Here
usually sulfur-containing compounds, as a rule saccharin, are added
to the bath for increasing hardness, which are incorporated into
the layer. That the nickel possesses but a very restricted heat
resistance as a consequence of the sulfur content and already
becomes embrittled somewhat above 200.degree. C. is mentioned as a
disadvantage of this method, since the S shifts the
recrystallization temperature of the galvanic nickel to lower
values. Due to the recrystallized nickel layer with a low hardness,
the entire layer system breaks with a punctiform load.
In the publication "Progress report of the VDI, On the
Microstructure and the Properties of Galvanically Precipitated
Nickel Layers" (Muller, p. 73 76, 1987), tests with regard to the
behavior of electrolytically precipitated Ni layers from sulfamate
baths with and without the addition of saccharin in the current
density range from 0.5 to 16 A/dm.sup.2 are examined. The goal of
the work is, among other things, studying microcrystal faults in
the Ni layers. It is established that fine precipitations of
Ni.sub.3S.sub.2 forms on the grain boundaries at heat treatment
above 200.degree. C. This leads to an embrittlement of the material
with heat treatment at 250.degree. C. On account of the micro
internal stresses, only a slight change in the microstructure takes
place between room temperature and about 200.degree. C.
Nonetheless, with one hour annealings in the temperature range from
200.degree. C. to 400.degree. C., the layers recrystallize. Above
400.degree. C., the layers recrystallize with a diminution of
hardness. Excessively high incorporation rates of sulfur-containing
compounds into the galvanic nickel layer can lead to the
embrittlement of the nickel layers in connection with heat
treatments due to the formation of nickel sulfide particles.
Applying an Ni/Sn alloy layer to the material for drawing battery
cans to improve the contact of the cathode mass with the
pre-nickel-plated material through the formation of so-called
"micro-cracks" is proposed in EP 0 725 453 A1. The underlying idea
is to enlarge the surface and to make available a greater contact
surface therewith. The possibility of applying a hard Ni layer
beneath the Ni/Sn layer using sulfur-containing bright additives
and a temperature treatment is described. This generates further
micro-cracks in addition to the micro-cracks of the Ni/Sn alloy
layer during drawing, raising the output of the battery further.
Typical temperatures for the temperature treatment lie above
400.degree. C.
In sum, the state of the art can be judged to the effect that all
temperature treatments which embrittle nickel speak of
recrystallization in which a migration of non-metallic elements,
such as C and S, into the grain boundaries takes place. The
non-metallic elements embrittle the grain boundaries, especially
with the formation of compounds (foreign substances) with the
surface coating metal, and with a subsequent transformation
process, preferably with deep drawing and iron drawing, the grain
boundaries tear and small micro-cracks are formed. These
micro-cracks have, as already explained, a decisive advantage above
all in batteries, since as low an electrical conductance resistance
as possible is desirable on the internal surface to avoid
unnecessary losses.
SUMMARY OF THE INVENTION
The invention is based upon the objective of attaining a method for
improving the embrittlement of such surface coatings for cold
rolled steels which can be subjected to deep drawing, preferably
for the manufacture of metal sheets for battery cans.
It is proposed as a realization of this objective that the
temperature selected for heat treatment lie beneath the
recrystallization temperature of the surface coating and above the
precipitation temperature for compounds which accumulate on the
grain boundaries and which consist of non-metallic elements and
surface coating metal.
Due to the advantageous selection of heat treatment of the surface
coating in which the temperature is high enough for precipitation
of compounds of the coating metal and non-metallic elements, but
still no recrystallization of the surface coating takes place, an
optimal embrittlement of the grain boundaries of the surface
coating is guaranteed without having recourse to battery poisons
such as tin. The disadvantage of the previously known methods with
associated recrystallization consists in the thickness of the
coating, which generally is in the same order of magnitude as the
grain size of the recrystallizing surface coating. Since the
compounds on the grain boundaries are precipitated, a
recrystallization of the coating leads to a migration of the
non-metallic component out of the coating and the embrittlement is
at least in part restored. Furthermore the number of grain
boundaries in the coating is reduced by a recrystallization on
account of grain enlargement. If one avoids recrystallization
during heat treatment, then the grain boundaries are preserved and
the brittle surface coating tears with the subsequent reforming of
the material. A subsequently applied carbon-containing coating for
diminishing the internal resistance of the battery or the cathode
material of an alkaline Zn/MnO.sub.2 battery, for example, adheres
very well to the surface so cracked. This overall leads to an
improvement of the conductivity of the battery, especially for
applications in which high currents are needed.
DETAILED DESCRIPTION
The following Tables 1 and 2 illustrate, on the basis of some
examples, at which temperatures heat treatment should take place in
order to attain a maximal crack formation in the coating. The heat
treatment is conducted at a temperature just below the
recrystallization temperature, in order to guarantee a most rapid
as possible precipitation of the embrittled compounds without the
embrittled compounds migrating out due to a recrystallization of
the coating.
Ni coating structures can be inferred from Table 1 as a function of
temperature.
TABLE-US-00001 TABLE 1 Ni coating structures Temperature Structure
of Additive # treatment [.degree. C.] Hardness Coating Free of
additives 1A -- 200 Stem 1B 360 177 Stem 1C 390 149 Beginning of
recrystallization TSA 2A -- 557 Stem 2B 240 530 Stem +
precipitation 2C 270 575 Stem + precipitation 2D 300 385
Recrystallized 2E 380 357 Recrystallized Saccharin 3A -- 484 Stem
3B 250 500 Stem 3C 330 262 Recrystallized Butindiol 4A -- 484 (493)
Stem + layers 4B 360 471 (483) Stem + layers 4C 400 424 Stem +
layers 4D 430 251 Beginning of recrystallization Butindiol + 5A --
857 Laminar saccharin 5B 290 765 Laminar 5C 320 773 Laminar 5D 350
418 Recrystallized
The Ni coating structures were determined on the basis of
micrographs of galvanized coatings. The coatings were ascertained
in various baths without and with additives such as TSA (toluene
sulfonamide), saccharin and butindiol. The samples in each group
designated with A were not heat treated. If one regards by way of
example the sample series 5A to 5C, one will note that a
temperature for heat treatment under 320.degree. C. ensures an
optimal crack formation. On the basis of the indicated hardness
data, it can be established that even small temperature changes
bring about significant differences of hardness in the coating.
Thus the hardness of the coating can be optimized in addition to
the brittleness through a compromise.
Table 2 illustrates the Co coating structures as a function of
temperature. The samples were evaluated with the aid of
micrographs, as were those from Table 1. The results allow a good
determination of optimal precipitation temperatures just under the
recrystallization temperature. No recrystallization could be
determined for the additives TSA and butindiol in the coating bath,
even for comparatively high temperatures.
TABLE-US-00002 TABLE 2 Co coating structure Temperature treatment
Hardness Structure of Additive # [.degree. C.] HV 0.2 the coating
Free of additives 6A 289 Stem (coarse) 6B 420 300 Stem (coarse) 6C
490 286 Stem (coarse) 6D 520 256 (50%) recrystallized 6F 550 274
Recrystallized TSA 7A 274 Stem (coarse) 7B 400 270 Stem (coarse) 7C
480 271 Stem (coarse) Butindiol 9A 352 Stem (very fine) 9B 380 400
Stem (very fine) 9C 410 418 Stem (very fine) Butindiol + 10A 326
Stem + layers saccharin 10B 240 379 Stem + layers 10C 360 350 (10%)
recrystallized 10D 430 406 (50%) recrystallized 10E 460 411
Recrystallized
An advantageous configuration of the invention provides that the
carbon content of the cold rolled strip lies under 0.5%. A further
advantageous refinement of the invention provides that a
prefinishing layer of Ni and/or Co or of a multilayer system on the
basis of these elements is applied to the cold rolled strip prior
to surface coating. It is especially appropriate for the
prefinishing layer be diffusion annealed. But it can also be
advantageous to apply the prefinishing layer using diffusion
precipitation. It is especially suitable for the prefinishing layer
to be applied as a C--Ni dispersion layer or as a C--Ni/Co alloy
dispersion layer. It is moreover suitable to apply a dispersion
coating and finally a surface coating after the diffusion-annealed
prefinishing layer, whereby it is furthermore appropriate in
accordance with the invention for the dispersion layer to be
applied as a C--Ni dispersion layer or as a Ni/Co alloy dispersion
layer. These various prefinishing layers under the surface coating
have advantages, especially for corrosion resistance and
conductivity.
Further advantageous features of the invention provide that instead
of C and S, P is incorporated as a non-metallic element in the
embrittled surface coating or a mixture of P, C and/or S, or that
instead of C and S, N is incorporated as a non-metallic element in
the embrittled surface coating, or a mixture of N, C and/or S
and/or P. Although mostly C and S are incorporated into the
coatings, it can be if need be advantageous to incorporate other
non-metallic elements, especially P and N, into the surface
coating, since these likewise act in an embrittling manner, but
otherwise have different effects on the properties of the
coating.
A further advantageous feature of the invention provides that the
surface coating is selectively embrittled by temperature treatment
according to the included non-metallic component. By a suitable
choice of temperature and an amount of previously mentioned
non-metallic elements set into proportion to this, the desired
hardness of the surface can be set in addition to the formation of
brittleness.
The device claims of the invention relate to a metal sheet or a
battery can, which are associated with the method of the invention
and to which the already mentioned advantages apply.
* * * * *